Universal driveline fluids are used to lubricate manual transmissions as well as final drive gear assemblies.
In manual transmissions, the choice of materials making up the synchronizer can influence performance. However, the lubricating fluid also plays a critical role. Manual transmission fluids require frictional retention properties to avoid a phenomenon known as synchronizer clashing (sometimes referred to as crashing). Clashing of the synchronizer results when the dynamic coefficient of friction building between the engaging synchronizer parts (plate to plate or ring to cone) falls below a critical minimum value. Below this critical minimum value the synchronizer parts do not attain zero relative velocity and the lockup mechanism (e.g., spline camphers) contacts the rotating member (e.g., cone camphers) resulting in a loud noise (clashing/crashing).
Final drive gear assemblies generally employed today are a hypoid gear arrangement. The hypoid gear involves extensive sliding motion. The sliding motion squeezes out the lubricant between the gears resulting in boundary lubricating conditions. In boundary lubrication conditions, lubrication occurs between two rubbing surfaces without the development of a full-fluid lubricating film. These conditions contrast to hydrodynamic lubrication conditions where a full-fluid lubricating film is maintained between the surfaces. A lubricant must provide effective extreme pressure and antiwear protection under boundary lubrication conditions. This is particularly important in an area where the final drive gear assembly is operated under low speed-high torque conditions or is subjected to high speed and shock loading conditions.
Generally when a lubricant is formulated to solve the requirements of a manual transmission, it lacks the necessary extreme pressure protection for hypoid gears. When a lubricant is formulated for a final drive gear assembly, it often lacks the friction properties necessary for a manual transmission.
U.S. Pat. No. 4,792,410 issued to Schwind et al relates to lubricant compositions suitable for manual transmission fluids.
U.S. Pat. No. 4,744,920 issued to Fischer et al relates to carbonated overbased products which are borated and processes for making the same.
U.S. Pat. No. 3,929,650 issued to King et al discloses borated overbased alkali metal carbonates of metal sulfonates.
U.S. Pat. No. 3,480,548 issued to Hellmuth et al discloses overbased boronated products.
U.S. Pat. No. 3,679,584 issued to Hellmuth relates to overbased alkaline earth metal sulfonates reacted with boric acid.
U.S. Patents 4,119,549 and 4,191,659 issued to Davis and U.S. Pat. Nos. 4,119,550 and 4,344,854 issued to Davis et al relate to sulfurized compositions prepared by the reaction of olefin compounds with a mixture of sulfur and hydrogen sulfide.